The present disclosure generally relates to treatment fluids for reducing subterranean formation damage, and, more specifically, to treatment fluids including an inclusion complex comprising a cyclodextrin compound and an acid precursor ester capable of delayed acid dissolution of formation damage.
Treatment fluids may be used in a variety of subterranean treatment operations. Such treatment operations may include, without limitation, drilling operations, completion operations, stimulation operations, production operations, remediation operations, sand control operations, and the like. As used herein, the term “treatment,” and all of its grammatical variants (e.g., “treat,” “treating,” and the like), refers to any subterranean formation operation that employs a fluid in conjunction with achieving a desired function and/or for a desired purpose. Use of these terms does not imply any particular action by the treatment fluid or a component therein, unless otherwise specified herein. More specific examples of illustrative treatment operations may include, but are not limited to, hydraulic fracturing operations, gravel packing operations, acidizing operations, scale dissolution and removal operations, consolidation operations, and the like.
During treatment operations, the subterranean formation being treated may experience formation damage. As used herein, the terms “formation damage” or “damage,” and all of their grammatical variants, refer to a reduction in the permeability of the formation in the near wellbore region, such as by deposition of a filtercake, natural or intentional, on the face of the formation. As used herein, the terms “formation damage” and “filtercake” may be used interchangeably. As used herein, the terms “particulate bridging material” or “bridging material,” and all grammatical variants thereof, refer to any particulate material, whether naturally present in a subterranean formation or introduced into a subterranean formation, that causes formation damage (i.e., reducing the permeability of the formation).
Because formation damage may occur during various treatment operations, such damage may accordingly arise at various stages of the lifecycle of the formation. Formation damage during drilling may be caused by a number of mechanisms including, for example, saturating the formation in the near wellbore region with fluids (e.g., aqueous fluids) from drilling fluids due to fluid loss, altering the wettability of the formation to oil-wet due to interactions with drilling fluid additives such that the formation preferentially imbibes oil, blocking the pore throats of the formation with solids or other precipitated compounds (e.g., metal ions) from drilling fluids and/or the formation, and the like.
During production of a wellbore in a subterranean formation (e.g., hydrocarbon production), formation damage may be undesirable as the highest pressure drops during production occur at the damaged near wellbore region. The damage causes a positive skin factor, or increased flow resistance, in the near wellbore region, which may reduce the productivity index of the wellbore (i.e., the ability of a reservoir in the formation to deliver fluids to the wellbore). Such a reduction in the productivity index may translate directly into economic costs for a wellbore operator, in terms of reduced fluid recovery (e.g., hydrocarbons), costly remedial operations such as expensive well stimulations, increased operator work time associated with remedial operations, and the like.
Conventional breakers used to remove formation damage involve use of very corrosive acids that interact with the particulate bridging material. Such corrosive acids may pose significant environmental, health, and safety risks and require specialized equipment (e.g., tubing, transportation and storage tanks, transportation trucks, and the like). The corrosive acids may additionally result in uncontrolled and immediate reactions with the formation damage, resulting in localized removal of the damage rather than a desired large expanse of damage. That is, the corrosive acid immediately reacts and is spent in a localized interval prior to reaching other locations downhole for formation damage removal. Additionally, the corrosive acids may increase the risk of wormholing. As used herein, the term “wormholing” or “wormhole,” and all grammatical variants thereof, refers to a large, empty channel that can penetrate several feet into a formation caused by non-uniform removal or dissolution of formation damage.
Esters have also been used as slow-release materials that hydrolyze to form acids capable of removing or dissolving formation damage over long intervals in a subterranean formation, due to their delayed acid release capability. The action of the esters may be delayed for several hours in normal circumstances. However, the presence of certain additives in the subterranean formation may hasten their action, such as breakers. Moreover, as the temperature of a downhole environment increases, such as in deeper and deeper wells which are becoming commonplace, the action of the ester is greater hastened, thereby defeating the beneficial slow-release of acid using the esters.